Preparing lithographic plates for printing



Patented Jan. 16, 1940 UNITED STATES PATENT OFFICE William 11. Wood, Bedford, om, assignor to Harria-Seybold-Potter Company, Cleveland, Ohio. a corporation of Delaware No Drawing. Application June 16, 1937, Serial No. 148,564

23 Claims. (Cl. 101-149) In common methods of preparing plates of lithographic printing, the plate usually of zinc or aluminum is coated with a water solution of albumin which has previously been made sensitive l to the action of light by the addition of a sensitizing agent such as ammonium chromate or dichromate. After the plate has been coated and allowed to dry, it is exposed to light in the form of an image of the subject to be printed. The

10 light hardens the albumin coating to the solvent action of water, thus forming a reproduction of the subject in hardened albumin and leaving the remaining portion of the albumin coating relatively unhardened. A suitable developing ink is ap- 1 plied to the coating and then'the unhardened areas are removed by dissolving them away with water. After application of an etching solution to clean the non-image portions of the plate and render them receptive to water, the plate is in I go condition for printing. In order tomaintain the plate in proper condition during printing, it is .necessary to apply thereto water or other dampening fluid by means of a suitable fountain.

The present invention has as its object an'im- 25 proved method of preparing and preserving plates for printing in the lithographic manner, involving the use of a new and much more effective agent both for treating the metal plate bearing -the image preliminarily to printing and as a dampening fluid for application'to the plateduring the printing operation.

To the accomplishment of the foregoing and related ends, said invention, then, consists of the steps and ingredients hereinafter fully described and particularly pointed out in the claims, the following description setting forth in detail certain steps 'and compositions of matter exemplifying my invention, such disclosed procedure and compositions constituting, however, but several m of various applications of the principle of the invention.

I have found that compounds providing an acrylic radical, such as acrylic acid or certain alkylated derivatives thereof, as for instance alphamethyl-acrylic acid, or their corresponding salts, such as the ammonium salts,'polymerized in such a way as to be water soluble, by which term is also connoted such a compound in water-dispersible form', provide excellent agents or media to so be applied to the non-printing portions of such lithographic plates, making suchportions water attracting'and highly ink repelling." An agent or medium having the composition just described is equally effective and desirable for application to the plate prior to the printing operation and as a dampening-fluid to be fed to or applied to the plate during the printing operation. Where used as a dampening fluid, the agent in the form of a solution or dispersion may be fed to the plate in any known manner. 5

It is possible by using the polymerized acids or salts above mentioned to eliminate entirely gum arabic, phosphoric acid, chromic acid and similar" materials from the etching fluids or plate dampening fluids which are at present used in printing from lithographic plates. However, water soluble salts of phosphoric acid or chromic acid may be added to the above named compounds if desired for use in the dampening fluid.

When lithographic plates are treated with the polymerized acids or salts above mentioned and printed in the known manner, many characteristics are discernible which show them to be superior to plates etched and dampened in accordance with the present practice. For example, plates thus treated require from to per cent. less dampening fluid during printing, this resulting in a superior print being obtained because there is less emulsiflcation of the ink by excess water and fuller intensity of color is realized. Moreover, the plates may be allowed to stand idle on the press for hours without any oxidation occurring, whereas such procedure would ruin plates treated-in the known way, unless a coating of gum arabic were applied and maintained othereon at all times except when the plate is actually being used for printing.

A further distinguishing characteristic resulting from my new and improved method of and agent for treating lithographic plates isthat the etching away of the plate surface, such'as results"1, from known etching and plate-dampening operations, is substantially entirely eliminated, thereby Y increasing the life of the plate on the press. The

relatively weak acid character of the polymer or its salts also helps in preventing the image disintegration that invariably takes place when the strong acids currently employed in the etching operation are applied.

The concentration of the polymer or its salts, whether applied to the plate directly in preparing the same for printing or by means of the water fountain during the printing operation,--isis.;.- not critical, but concentrations of from i tot-.10 per cent. are ordinarily sumcient. For certain 50 types of printing where excessively greasy inks are employed, it may be desirable to add a small quantity of a mild organic acid to the solution of polyacrylic acid or its salts, such addition assisting in keeping the plate and dampening rolls tree of scum. Suitable organic acids for such use are gluconic acid or an equilibrium mixture thereof with glucono lactones and pyruvic or levulinic acid.

Polyacrylic acid may be obtained in the form of a viscous clear solution in water varying in concentration from 15 to 50 per cent. by weight. For treating lithographic plates preliminarily to printing, such solution of the acid, or corresponding salt, e. g., the ammonium salt, will preferably be diluted to form a solution of from 2 to 5 per cent. A mixture of the acid and salt can be used; indeed the pH of the solution may be conveniently controlled by neutralizing it to the desired degree. Preferably the solution should be approximately neutral, although it can go on the alkaline side as far as pH 8. For use as a dampening fluid a still more dilute solution of the acid or salt will preferably be employed, for example from 0.04 to 0.10 per cent. up to a maximum oil per cent. Where a weak organic acid, as hereinbefore described, is added to such dampening solution, it will be added in amount approximately equal to the polyacrylic acid orsalt thereof. If a soluble salt of phosphorus or chromium be used, this will be in addition to the organic salt and in somewhat lesser amount, for example one-tenth. All of the foregoing proportions and amounts are'by weight.

It will be understood that my improved agent or medium for treating lithographic plates is not necessarily limited to plates of the conventional type, i. e., having an albumin coating; also that the precise order in which the steps involved in preparing such plate may be varied and in particular that such agent or medium may be employed for treating the plate in the preparatory stage or for dampening the finished plate during printing, or both, as may be desired.

Other modes of applying the principle of the invention may be employed, change being made as regards the composition and method described, provided the ingredients or steps stated in any of the following claims, or the equivalent of such stated ingredients or steps, be employed.

I therefore particularly point out and distinctly claim as my invention:

1. In the process of preparing plates for printing in lithographic manner, treating the imagebearing metal plate with a solution providing a polyacrylic compound.

2. In the process of preparing plates for printing in lithographic manner, treating the imagebearing metal plate with-a solution containing polyacrylic acid.

3. In the process of preparing plates for printing in lithographic manner, treating the imagebearlng metal plate with a solution containing polyacrylic acid neutralized at least in part with a base.

4. In the process of preparing plates for print ing in lithographic manner, treating the image-' bearing metal plate with a solution containing an alkylated acrylic compound.

5. In the process of preparing plates for printing in lithographic manner, treating the imagebearing metal plate with a solution containing alpha-methyl-acrylic acid.

6. In the process of preparing plates for printing in lithographic manner, treating the imagebearing metal plate with a solution providing a polyacrylic compound and a water-soluble radical of an organic acid having the mild acid character of gluconic acid.

7. In the process of preparing plates for printing in lithographic manner, treating the imagebearing metal plate with a solution providing a polyacrylic compound and a water-soluble salt of an acid from the group consisting of phosphoric and chromic acids.

8. In the process of preparing plates for printing in lithographic manner, treating the imagebearing metal plate with.a solution providing a polyacrylic compound and a mild organic acid from the group consisting of gluconic acid, mixtures of gluconic acid and glucono-lactones, mixtures of gluconic and pyruvic acids, and mixtures of gluconic and levulinic acids.

' 9. In the process of preparing plates for printing in lithographic manner, treating the imagebearing metal plate with a. solution providing a polyacrylic compound and a mild organic acid from the group consisting of gluconic acid, mixtures of gluconic acid and glucono-lactones, mixtures of gluconic and pyruvic acids, and mixtures of gluconic and levulinic acids, and a watersoluble salt of an acid from the group consisting of phosphoric and chr'omic acids.

10. In the process of preparing plates for printing in lithographic manner, treating the image-bearing metal plate with a solution of polyacrylic acid and gluconic acid.

11. A process of dampening metal plates for lithographic printing with a solution providing a polyacrylic compound.

12. A process of dampening metal plates for lithographic printing with a solution containing a polyacrylic acid.

13. A process of dampening metal plates for lithographic printing with a solution containing polyacrylic acid neutralized at least in part with a base.

14. A process of dampening metal plates for lithographic printing with a solution containing an aikylated acrylic compound.

15. A process of dampening metal plates for lithographic printing with a solution containing alpha-methyl-acrylic acid.

16. A process of preparing plates for printing in lithographic manner, which comprises treating the image-bearing plate with a solution containing about 1 to 10 per cent of a polyacrylic compound.

17. In lithographic printing, dampening the lithographic plate with a solution containing about 0.04 to 1 per cent of a polymer of an acrylic radical.

18. As a new product, a lithographic plate having a water-receptive organic colloid surface portion comprising a polymer of an acrylic radical.

19. As a new product, a lithographic plate having a water-receptive organic colloid surface portioncomprising a polymerized alkylated acrylic compound.

'20. As a new product, a lithographic plate having a water-receptive organic colloid surface 23. As a new product, a. lithographic plate having a water-receptive organic colloid surface portion comprising a polymer of an acrylic radical,

of gluconic and pyruvic acid, and mixtures of gluconic and levulinic acids, and also containing a water-soluble salt of an acid from the group consisting of phosphoric and chromic acid.

WILLIAM H. WOOD. 

